I have switched to using a tablet (old iPad) plus remote control app instead of button-loaded hardware for various reasons:
1. I want to enter chords, not only monophonic melodies
2. I want more than 16 steps
3. I want to see where the white and black keys of the keyboard are

To fulfill all that, you would need a really monstrous hardware device that will always be unflexible.

There's plenty of DIY sequencer templates for Liine Lemur, for example, and you can modify them or build your own in any way you like. But there are many other apps too...